The invention relates to a medical assembly comprising a short catheter, a puncturing needle engaged in the catheter to enable the catheter to be inserted into a body, and a tubular sheath detachably coupled to the catheter to receive the entire needle after the needle has been used for puncturing and once it has been withdrawn from the catheter.
Numerous embodiments of such an assembly are known (U.S. Pat. Nos. 5,273,540, 6,077,244, 6,193,690, 5,879,331, WO 95/19193).
Publications U.S. Pat. No. 5,879,331 and WO 95/19193 describe embodiments in which the sheath presents a longitudinal slot between a distal outlet for connection to the catheter and an opposite proximal end, and carries a slider mounted to slide along the slot, the slider presenting an internal portion situated inside the sheath and constituting a base for the needle, and an external portion situated on the sheath and enabling the slider to be moved manually so as to cause it to slide from a distal position in which the needle passes through the catheter to a proximal position in which the needle is totally withdrawn from the catheter and retracted into the sheath.
The problem arises of ensuring that once the needle has been retracted into the sheath in this way and after the sheath and the catheter have been separated, it is not possible under the effect of inappropriate handling of the slider for the needle to be moved back out from the sheath through the coupling outlet, and various solutions have been proposed for this purpose.
In the solution described in U.S. Pat. No. 5,879,331, the sheath is provided with a moving arm which tilts when it is contacted by the slider, and presses against the needle close to its sharp end so as to incline the needle in such a manner that it is no longer on the axis of the catheter coupling outlet.
In an embodiment described in publication WO 95/19193 the sheath is shaped internally, close to the end of the stroke of the slider towards said proximal end of the sheath, so that, at the end of the stroke, contact between the slider and the sheath causes the slider to be inclined and consequently causes the needle to be inclined inside the sheath.